Improving the sorption properties of mesoporous carbons for the removal of cobalt, nickel and manganese from spent lithium-ion batteries effluent

The competitive sorption of Co2+, Li+, Ni2+, and Mn2+, strategic metals from spent lithium-ion batteries and their leachates, was studied using activated mesoporous carbons. The mesoporous carbon was synthesized by the replica method using silica gel as a template and exhibited a high surface area with an accessible pore volume due to mesopores (Vmeso > 95%). Fast kinetics and high sorption capacities of these metals were achieved with the chemical activation of mesoporous carbons. The surface modification of the mesoporous carbon was carried out by physical activation with O2 at 450 °C and chemical activation under mild conditions (room temperatures) with NaClO2/H2O2 as oxidizing agents. FTIR analysis and conductimetric titration showed that the combination of an initial physical activation step, followed by chemical functionalization, maximized the formation of carboxylic acids (from 0.2 to 0.9 meq/g), due to the complete oxidation of the weakly acidic groups. Those carbons were tested in sorption experiments of the lithium-ion battery metals in monometallic solutions, where physically activated and chemically reactivated mesoporous carbon selectively removed over 80% of Co2+, Ni2+, and Mn2+, with sorption capacities over 20 mg/g, while only 20% of Li+ was removed. This carbon stood out amongst the others studied (2 to 11-fold increase in sorption capacities depending on the metal) and was tested in multimetallic solutions, showing fast removal rates, reaching equilibrium within the first 15 min, as well as selectivity towards divalent cations (18 mg/g of Co2+) with insignificant lithium sorption (qLi = 0.33 mg/g). Desorption of metals was carried out using H2SO4, which allowed the recovery and twofold of the initial concentrations of Co, Ni, and Mn.